The fire erupted in the dialysis ward of the SUM hospital's critical-care unit in the state capital, Bhubaneswar, public health officials said.

Preliminary information showed the fire started after an electrical short-circuit, media said.

Many of the 19 dead were elderly people who had suffocated to death, C. R. Nayak, the state's director of health services, told Reuters.

Ambulances took more than 120 patients to other hospitals, officials said, while firemen battled to control the flames.

Some of the wounded patients were still in critical condition.

"We are trying our best to save lives," said Arti Ahuja, an official of the state's health and family welfare department.

The tragedy was "mind-numbing", said Prime Minister Narendra Modi, who urged the federal health minister to hasten the transfer of injured victims to a nearby government hospital, the All India Institute of Medical Sciences.

"Deeply anguished by the loss of lives in the hospital fire," Modi said on social network Twitter.